Hi, Sorry to bring this back up but I'm still stumped, and I feel very
close!! Thomas I took your suggestion and changed the 'out' to 'in'.
From:
COMMETHOD([], HRESULT, 'Read',
( ['out'], POINTER(c_ubyte), 'data' ),
( ['in'], c_int, 'len' ),
( ['out'], POINTER(c_int), 'actual' )),
...]
To:
COMMETHOD([], HRESULT, 'Read',
( ['in'], POINTER(c_ubyte), 'data' ),
( ['in'], c_int, 'len' ),
( ['out'], POINTER(c_int), 'actual' )),
...]
However defining it this way, it now seems to expect a single c_ubyte
instead of a pointer to a c_ubyte.
When I try:
data = POINTER(c_ubyte)()
res = y.Read(byref(data), len)
I get this exception, which seems odd since we defined it as
POINTER(c_ubyte) in the type library:
ctypes.ArgumentError: argument 1: <type 'exceptions.TypeError'>:
expected LP_c_ubyte instance instead of pointer to LP_c_ubyte
However, when I try:
data = c_ubyte()
res = y.Read(byref(data), len)
then it executes successfully, but of course data only has 1 value and
Python crashes after the next Read attempt.
I think maybe I need to redefine to something else?
Thanks again for your help so far.
On Thu, Jun 18, 2009 at 11:57 AM, px<p...@qualm.net> wrote:
> Thanks Thomas. I tried your suggestion and changed out to in but it seems
> to not expect a pointer
>
> COMMETHOD([], HRESULT, 'Read',
> ( ['in'], POINTER(c_ubyte), 'data' ),
> ( ['in'], c_int, 'len' ),
> ( ['out'], POINTER(c_int), 'actual' )),
> ...]
>
> --
>
> data = POINTER(c_ubyte)()
> len = 2
> res = y.Read(byref(data), len)
>
> ArgumentError: argument 1: <type 'exceptions.TypeError'>: expected
> LP_c_ubyte instance instead of pointer to LP_c_ubyte
>
>
>
> On Wed, Jun 17, 2009 at 2:06 AM, Thomas Heller <thel...@ctypes.org> wrote:
>>
>> px schrieb:
>> > Thanks Thomas! This was very helpful indeed. Working great now :)
>> >
>> > Came across another problem trying to read back an unsigned byte
>> > buffer..
>> > I'm pretty stumped
>> >
>> > # COMMETHOD([], HRESULT, 'Read',
>> > # ( ['out'], POINTER(c_ubyte), 'data' ),
>> > # ( ['in'], c_int, 'len' ),
>> > # ( ['out'], POINTER(c_int), 'actual' )),
>> >
>> > When I call Read(2048), I always just get 13 back for the data field
>> > (first
>> > element in returned tuple) but I actually expect more bytes.
>> >
>> > I took a shot at doing a ctypes style call, but when I try to make the
>> > call
>> > x.Read(byref(data), len, byref(actual))
>> > I get
>> > TypeError: call takes exactly 2 arguments (4 given)
>> >
>> > It seems that comtypes only wants the in 'len' parameter.
>> >
>> >>From the IDL:
>> > HRESULT Read(
>> > [out, size_is(length), length_is(*actual)] BYTE* data,
>> > [in] long length,
>> > [out] long* actual);
>>
>> comtypes isn't able to handle the 'length_is(...)' attribute. Besides,
>> the info from this attribute isn't present in the TLB at all. So,
>> you should override the generated 'Read' method in this way,
>> which passes the pointer as 'in' argument, and later unpacks it:
>>
>>
>> COMMETHOD([], HRESULT, 'Read',
>> ( ['in'], POINTER(c_ubyte), 'data' ),
>> ( ['in'], c_int, 'len' ),
>> ( ['out'], POINTER(c_int), 'actual' )),
>> ...]
>>
>> def Read(self, len):
>> data = POINTER(c_ubyte)()
>> actual = self._Read(byref(data), len)
>> result = data[:actual]
>> # I guess you need to free the memory here?
>> # windll.ole32.CoTaskMemFree(data)
>> return result
>>
>> Thomas
>>
>>
>>
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